This invention relates to improvements in the operating system, method and apparatus for flat belt continuously variable transmission systems utilizing variable ratio pulleys. Such pulleys are of the nature disclosed in U.S. Pat. Nos. 4,295,836, Oct. 20, 1981 and 4,591,351, May 27, 1986, Emerson L. Kumm, and it is an object of the invention to provide an improved system method and apparatus of the nature indicated. The disclosures of these two patents are incorporated by reference into this specification. Systems of the nature disclosed in the two patents referred to utilize two variable ratio pulleys connected by a flat belt.
The variable ratio is achieved by making each pulley of two pairs of pulley disks, one pair of which is inside of the other pair such that the space between the inner pulley disks defines a space within which the flat belt runs. The inner pulley disks of each pulley are connected rigidly together so as to run as a unit and each pulley disk has logarithmic spiral guideways in it. The two outer pulley disks are also connected together as a unit and each of them includes logarithmic spiral guideways therein. The spiral guideways of the inner set of pulley disks are directed in one sense, clockwise or counterclockwise proceeding to larger radii, and the logarithmic spiral guideways in the outer set of pulley disks are directed in the opposite sense. Thus the guideways of the pulley disks adjacent each other on each side of the pulley form intersections. Belt drive elements are disposed between the intersections around the full circumference of the pulleys and thus the belt engaging the drive elements causes one pulley to drive the other.
The properties of the logarithmic spiral guideways are those as described in the patents referred to and the intersections of the guideways in the inner and outer guideway disks are at right angles to each other, that is, at ninety degrees. In the U.S. Pat. No. 4,295,836 the directional sense of the logarithmic spiral guideways with respect to the direction of the belt movement is the same for the drive pulley as the driven pulley. In the U.S. Pat. No. 4,591,351 the showing of the logarithmic spiral guideways in one directional sense in one pulley and in the opposite directional sense in the other pulley is an incidental fact not related to the present invention. In neither case is there an awareness of the relationship between the sense or direction of the logarithmic spiral guideways and the hydraulic pressure necessary to rotate one set of guideway disks relative to the other set of guideway disks for changing the diameter of the pulley, or that the direction of movement of the belt also affects the required hydraulic operating pressure.
The applicant has discovered that the required hydraulic pressure is reduced to a minimum if the directional sense of the logarithmic spiral guideways connected directly to the shaft of the driving pulley are opposed to the direction of belt movement and the logarithmic spiral guideways which are connected directly to the shaft of the driven pulley are in the same sense as the direction of belt movement.
It is an object of the invention to provide improved apparatus and system which takes advantage of this discovery in making continuous variable transmission drives of the nature involved in this application.